The present invention is related to in general WDM (Wavelength Division Multiplexing) optical network systems and, more particularly, to systems and methods for protecting the loss of through communication channels at an add/drop node in the event of a power failure.
In WDM systems, multiple optical signals having different wavelengths share an optical fiber, each wavelength defining a particular communication channel. Hence WDM systems include any system using optical wavelengths to define channels, such as DWDM (Dense Wave Division Multiplexing). This technique of wavelength division multiplexing has many advantages in implementing optical communication systems, including increased capacity and the ability to use passive optical components to redirect a portion of the data flowing along the optical fiber for processing at an intermediate node.
A representative WDM system may include multiple nodes connected to one another by optical fiber. For example, the nodes may be connected in a ring. Each node typically uses only certain wavelengths (also referred to as WDM channels) for transmission and reception and leaves the other wavelengths untouched. The untouched wavelengths form through channels at the node. A WDM add/drop multiplexer isolates and removes (or “drops”) selected WDM channels from the optical fiber at a node. The channels that are dropped in this way are processed by receiver circuitry within the node or are otherwise rerouted. Signals may also be generated on these channels for transmission onto the fiber at the node. The add/drop multiplexer combines (or “adds”) these new signals to the through channels at the node. Hence the add/drop multiplexer implements the drop and add functions of the node, which itself is often termed an add/drop node on the optical fiber.
One problem for many of these add/drop multiplexers is their opto-electric components render the multiplexers susceptible to power outages. For example, reconfigurable add/drop multiplexers rely on opto-electric components to select the particular add or drop channels (and through channels). Changes in the selected channels can be made easily. A subtle point is that the opto-electric components control signal strengths in the through channels of the add/drop multiplexer. With power outages, the operation of the opto-electric components (and the add/drop multiplexer) is interrupted. Of course, a way of avoiding such interruptions to supply the add/drop multiplexers with uninterruptible power sources. This solution, however, considerably increases the costs of the multiplexers. Another solution is to avoid electrical components altogether; however, the resulting add/drop multiplexers are considerably restricted in the flexibility of their operations.
The present invention addresses this challenge with an add/drop multiplexer system which permits through channels to continue at a node despite a power outage at relatively low cost. In this manner only the node with the power loss is affected and the other interconnected nodes remain in operation to keep the optical network in operation.